U.S. patent application number 14/723155 was filed with the patent office on 2015-12-10 for driving-force controller for electric vehicle.
This patent application is currently assigned to MITSUBISHI JIDOSHA KOGYO KABUSHIKI KAISHA. The applicant listed for this patent is MITSUBISHI JIDOSHA KOGYO KABUSHIKI KAISHA. Invention is credited to Tetsuya FURUICHI, Akira HASHIZAKA, Yasuyuki HATSUDA, Ryosuke KOGA, Toshiyuki MATSUMI, Hiroaki MIYAMOTO, Toshifumi MIZUI, Sosuke NANBU, Masato NISHIDA, Takanori SUGIMOTO, Hideaki TANIGUCHI.
Application Number | 20150352978 14/723155 |
Document ID | / |
Family ID | 54768899 |
Filed Date | 2015-12-10 |
United States Patent
Application |
20150352978 |
Kind Code |
A1 |
HASHIZAKA; Akira ; et
al. |
December 10, 2015 |
DRIVING-FORCE CONTROLLER FOR ELECTRIC VEHICLE
Abstract
A driving-force controller for an electric vehicle including at
least two motors that independently drive left and right wheels,
includes a detector that detects driving operation by a driver, and
a controller that calculates a demand torque Tr of the driver, the
torque difference .DELTA.T applied to the left and right wheels
during cornering, left and right torque-difference maintaining
torques TL.sub.K and TR.sub.K of the motors when generating the
demand torque Tr while maintaining the torque difference .DELTA.T,
and controls the motors based on the torque-difference maintaining
torques TL.sub.K and TR.sub.K. The controller determines the
priorities of a demand torque mode that generates the demand torque
Tr and a torque difference mode that generates the torque
difference .DELTA.T depending on the driving operation detected by
the detector.
Inventors: |
HASHIZAKA; Akira; (Tokyo,
JP) ; MATSUMI; Toshiyuki; (Tokyo, JP) ;
MIYAMOTO; Hiroaki; (Tokyo, JP) ; TANIGUCHI;
Hideaki; (Tokyo, JP) ; SUGIMOTO; Takanori;
(Tokyo, JP) ; NISHIDA; Masato; (Tokyo, JP)
; MIZUI; Toshifumi; (Tokyo, JP) ; NANBU;
Sosuke; (Tokyo, JP) ; HATSUDA; Yasuyuki;
(Tokyo, JP) ; FURUICHI; Tetsuya; (Tokyo, JP)
; KOGA; Ryosuke; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBISHI JIDOSHA KOGYO KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Assignee: |
MITSUBISHI JIDOSHA KOGYO KABUSHIKI
KAISHA
Tokyo
JP
|
Family ID: |
54768899 |
Appl. No.: |
14/723155 |
Filed: |
May 27, 2015 |
Current U.S.
Class: |
701/22 |
Current CPC
Class: |
B60L 15/2036 20130101;
B60L 2240/423 20130101; B60L 3/12 20130101; Y02T 10/72 20130101;
Y02T 10/7275 20130101; Y02T 10/646 20130101; Y02T 10/645 20130101;
Y02T 10/64 20130101; B60L 2220/42 20130101 |
International
Class: |
B60L 15/20 20060101
B60L015/20; B60L 3/12 20060101 B60L003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 4, 2014 |
JP |
2014-115820 |
Jan 26, 2015 |
JP |
2015-012559 |
Claims
1. A driving-force controller for an electric vehicle comprising at
least two motors that independently drive left and right wheels,
the driving-force controller comprising: a detector that detects
driving operation by a driver; and a controller that calculates a
demand torque of the driver and a torque difference applied to the
left and right wheels during cornering, calculates left and right
torque-difference maintaining torques of the motors when generating
the demand torque while maintaining the torque difference, and
controls the motors based on the torque-difference maintaining
torques, wherein the controller determines priorities of a demand
torque mode that generates the demand torque and a torque
difference mode that generates the torque difference, depending on
the driving operation detected by the detector.
2. The driving-force controller according to claim 1, wherein, the
detector comprises an accelerator position sensor that detects the
stepping operation of an acceleration pedal as the driving
operation, and the controller acquires a degree of acceleration
requirement of the driver based on the stepping operation of the
accelerator pedal detected by the accelerator position sensor and
determines the priorities depending on the degree of acceleration
requirement.
3. The driving-force controller according to claim 2, wherein the
controller increases the priority of the demand torque mode as the
degree of acceleration requirement becomes larger during
cornering.
4. The driving-force controller according to claim 2, wherein the
controller increases the priority of the torque difference mode as
the degree of acceleration requirement becomes smaller during
cornering.
5. The driving-force controller according to claim 2, wherein the
controller selects the demand torque mode when the degree of
acceleration requirement is equal to or larger than a predetermined
value during cornering and selects the torque difference mode when
the degree of acceleration requirement is smaller than the
predetermined value during cornering.
6. The driving-force controller according to claim 1, wherein the
controller determines the priorities using a map previously setting
therein a relationship between the driving operation by the driver
and the torque difference of the left and right wheels, the torque
difference being generatable during cornering.
7. The driving-force controller according to claim 1, wherein the
controller determines the priorities depending on the driving
operation detected by the detector when a torque of the turning
outer wheel, being one of the left and right torque-difference
maintaining torques, exceeds a maximum output torque of the
motors.
8. The driving-force controller according to claim 1, wherein the
controller sets an output torque from one of the motors of the
turning outer wheel to a maximum output torque of the motors and
determines an output torque from the other one of the motors of the
turning inner wheel depending on the priorities, when a torque of
the turning outer wheel, being one of the left and right
torque-difference maintaining torques, exceeds the maximum output
torque.
9. The driving-force controller according to claim 1, wherein, the
detector comprises an accelerator position sensor that detects the
stepping operation of an acceleration pedal as the driving
operation, and the controller determines the priorities depending
on the stepping operation acceleration of the acceleration pedal
detected by the accelerator position sensor.
Description
CROSS-REFERENCE TO THE RELATED APPLICATION
[0001] This application incorporates by references the subject
matter of Application No. 2014-115820 filed in Japan on Jun. 4,
2014 and Application No. 2015-012559 filed in Japan on Jan. 26,
2015 on which a priority claim is based under 35 U.S.C.
.sctn.119(a).
FIELD
[0002] The present invention relates to a driving-force controller
for an electric vehicle including motors that independently drive
left and right wheels.
BACKGROUND
[0003] Electric vehicles have been known including motors that
independently drive the left and right wheels, which each consist
of at least one of forward and rearward wheels (refer to Japanese
Unexamined Patent Application Publication No. 2008-222070). Such a
driving system is referred to as twin-motor system or
left-and-right-independent-drive system and has been drawing
attention for its independent control of the driving forces
(torques) applied to the left and right wheels, which improves
kinematic performance. For example, a vehicle can generate a yaw
moment during cornering through a difference between the driving
forces (torque difference) applied to the left and right wheels in
addition to the steering angle, so as to improve the cornering
performance of the vehicle.
[0004] In the driving systems described above, the torque demanded
by the driver (demand torque) is distributed and generated to the
left and right motors. Thus, there is a problem which the torque
difference generated by the left and right motors becomes smaller
as the demand torque becomes larger. This is because, in general,
the motors installed in the vehicle output the substantial maximum
power when the demand torque is maximum. Thus, as the demand torque
becomes larger, the margin of the motor output becomes smaller.
[0005] That is, depending on the operation by the driver, the
driving systems described above can probably achieve a driver's
request, but may nullify the torque difference between the left and
right wheels during cornering. This interferes with the improvement
of the cornering performance. On the other hand, the torque
difference between the left and right wheels can be maintained
through a decrease in the output of one of the left and right
motors. In such a case, the decrease in the total output of the
motors causes an insufficient response to a driver's request.
SUMMARY
Technical Problems
[0006] An object of the present invention, which has been
accomplished to solve the above problems, is to provide a
driving-force controller for an electric vehicle that can improve
the cornering performance of the electric vehicle, while achieving
a driver's request. In addition to the object described above, any
other object of the present invention may be the achievement of
advantages through the configuration of the embodiments of the
present invention described below, which cannot be achieved by any
traditional art.
Solution to Problems
[0007] (1) The driving-force controller for an electric vehicle
according to the present invention is provided in an electric
vehicle that includes at least two motors that independently drive
left and right wheels. The driving-force controller includes a
detector that detects the driving operation by a driver. The
driving-force controller includes a controller that calculates a
demand torque of the driver and a torque difference applied to the
left and right wheels during cornering, calculates left and right
torque-difference maintaining torques of the motors when generating
the demand torque while maintaining the torque difference, and
controls the motors based on the torque-difference maintaining
torques. The controller determines priorities of a demand torque
mode that generates the demand torque and a torque difference mode
that generates the torque difference depending on the driving
operation detected by the detector.
[0008] (2) The detector preferably includes an accelerator position
sensor that detects the stepping operation of an acceleration pedal
as the driving operation. In such a case, the controller preferably
acquires a degree of acceleration requirement of the driver based
on the stepping operation of the accelerator pedal detected by the
accelerator position sensor and determines the priorities depending
on the degree of acceleration requirement.
[0009] (3) The controller preferably increases the priority of the
demand torque mode as the degree of acceleration requirement
becomes larger during cornering.
[0010] (4) The controller preferably increases the priority of the
torque difference mode as the degree of acceleration requirement
becomes smaller during cornering.
[0011] (5) The controller preferably selects the demand torque mode
when the degree of acceleration requirement is equal to or larger
than a predetermined value during cornering and selects the torque
difference mode when the degree of acceleration requirement is
smaller than the predetermined value during cornering.
[0012] (6) The controller preferably determines the priorities
using a map previously setting therein a relationship between the
driving operation by the driver and the torque difference of the
left and right wheels, the torque difference being generatable
during cornering.
[0013] (7) The controller preferably determines the priorities
depending on the driving operation detected by the detector when a
torque of the turning outer wheel, being one of the left and right
torque-difference maintaining torques, exceeds a maximum output
torque of the motors.
[0014] (8) The controller preferably sets an output torque from one
of the motors of the turning outer wheel to a maximum output torque
of the motors and determines an output torque from the other one of
the motors of the turning inner wheel depending on the priorities,
when a torque of the turning outer wheel, being one of the left and
right torque-difference maintaining torques, exceeds the maximum
output torque.
[0015] (9) The detector preferably includes an accelerator position
sensor that detects the stepping operation of an acceleration pedal
as the driving operation. In such a case, the controller preferably
determines the priorities depending on the stepping operation
acceleration of the acceleration pedal detected by the accelerator
position sensor.
Advantageous Effects
[0016] The driving-force controller for an electric vehicle
according to the present invention can improve the cornering
performance of the electric vehicle while achieving a driver's
request.
BRIEF DESCRIPTION OF DRAWINGS
[0017] The nature of this invention, as well as other objects and
advantages thereof, will be explained in the following with
reference to the accompanying drawings, in which like reference
characters designate the same or similar parts throughout the
figures and wherein:
[0018] FIG. 1 is a schematic block diagram illustrating an overview
of a driving-force controller for an electric vehicle according to
a first embodiment.
[0019] FIG. 2 is a block diagram illustrating the ECU in FIG.
1.
[0020] FIG. 3A is an example map for acquiring the demand torque.
FIG. 3B is an example map illustrating the output characteristics
of motors of the driving-force controller according to the first
embodiment.
[0021] FIG. 4 is a flow chart illustrating the control process
carried out by the driving-force controller according to the first
embodiment.
[0022] FIG. 5 is an example map for setting the upper limit torque
difference of the driving-force controller according to a second
embodiment.
[0023] FIG. 6 is an example map illustrating the output
characteristics of motors of the driving-force controller according
to the second embodiment.
[0024] FIG. 7 is a flow chart illustrating the control process
carried out by the driving-force controller according to the second
embodiment.
[0025] FIGS. 8A and 8B are example maps for setting the upper limit
torque difference in the driving-force controller according to
modifications.
DESCRIPTION OF EMBODIMENTS
[0026] Embodiments of the present invention will now be described
with reference to the accompanying drawings. The embodiments
described below are mere examples, and various modifications and
technological applications that are not described in the
embodiments should not be excluded from the scope of the invention.
The configurations of the embodiments may be modified in various
ways within the scope of the invention and may be selected and/or
be combined appropriately.
1. First Embodiment
1-1. Device Configuration
[0027] The driving-force controller for an electric vehicle
according to a first embodiment will now be described with
reference to FIGS. 1 to 4.
[0028] FIG. 1 is a schematic block diagram illustrating the
electric vehicle including the driving-force controller according
to this embodiment.
[0029] With reference to FIG. 1, a vehicle 1 (electric vehicle)
includes a left motor 2L that drives a left rear wheel 4L and a
right motor 2R that drives a right rear wheel 4R. The vehicle 1 is
a rear-wheel-independent-drive type electric vehicle that
independently drives the left rear wheel 4L and the right rear
wheel 4R. In this embodiment, the vehicle 1 is exemplified by a
rear-wheel-independent-drive type electric vehicle. Alternatively,
the vehicle 1 may be a front-wheel-independent-drive type electric
vehicle that independently drives the left front wheel 3L and the
right front wheel 3R. Hereinafter, the motors 2L and 2R, the front
wheels 3L and 3R, and the rear wheels 4L and 4R will be simply
referred to as motors 2, front wheels 3, and rear wheels 4,
respectively, unless they should be differentiated.
[0030] The motors 2L and 2R are motor generators, such as
three-phase synchronous motors or three-phase induction motors,
which can operate in a powered mode and a regenerative mode and
have identical output characteristics (driving-force
characteristics) described below. The motors 2 are driven by
electrical power supplied from a battery (not shown) via an
inverter (not shown) that converts the DC power to AC power. The
motors 2 are regeneratively driven by the rotation of the rear
wheels 4 to generate electric power that can be stored in the
battery.
[0031] Reducers 5L and 5R that reduce the rotational speed of the
motors 2 are disposed on the axels connecting the motors 2 to the
respective rear wheels 4. The front wheels 3L and 3R and the rear
wheels 4L and 4R include brake units 6L and 6R and brake units 7L
and 7R, respectively. The vehicle 1 also includes a brake
controller (not shown) that controls the brake units 6L, 6R, 7L,
and 7R and hydraulic units (not shown) in the braking system that
independently supply hydraulic pressure to the brake units 6L, 6R,
7L, and 7R on the basis of instructions from the brake
controller.
[0032] Wheel-speed sensors 13L and 13R and wheel-speed sensors 14L
and 14R are respectively provided near the front wheels 3L and 3R
and the rear wheels 4L and 4R to detect the wheel rotating speed.
The vehicle 1 also includes a steering angle sensor 15 (detector)
that detects the operation amount (driving operation) of a steering
wheel 8 by the driver (hereinafter referred to as steering angle
.theta.) and an accelerator position sensor 16 (detector) that
detects the stepping operation amount (driving operation, stepping
operation) of an accelerator pedal 9 by the driver (hereinafter
referred to as accelerator position AP). The values (sensor values)
detected by the wheel-speed sensors 13L, 13R, 14L, and 14R, the
steering angle sensor 15, and the accelerator position sensor 16
are sent to an ECU 10 described below.
[0033] The steering angle .theta. corresponds to the operation
direction of the steering wheel. A steering angle .theta. for
turning the vehicle 1 to the right is positive, and a steering
angle .theta. for turning the vehicle 1 to the left is negative.
The accelerator position AP corresponds to the output (hereinafter
referred to as demand torque Tr) required by the driver. That is, a
large output required by the driver (the request of the driver to
accelerate) increases accelerator position AP, whereas a small
output required by the driver (the request of the driver to
maintain constant speed or decelerate) decreases the accelerator
position AP.
[0034] The vehicle 1 includes an electronic control unit (ECU) 10
(controller), which is, for example, a microprocessor, an LSI
device having integrated ROMs and RAMs, or a built-in electronic
device. The ECU 10 is an electronic controller that integrally
controls the various devices equipped in the vehicle 1 and is
connected to a communication line in an in-vehicle network provided
in the vehicle 1. The driving-force control according to this
embodiment performed during cornering of the vehicle 1 will now be
described.
1-2. Control Configuration
[0035] Driving-force control is to determine priorities of two
control modes depending on the driving operation by the driver
during cornering, and to set output torques TL and TR of the motors
2L and 2R, respectively, depending on the priorities, and to drive
the motors 2. The driving-force control has two control modes: a
demand torque mode in which priority is given to the generation of
the output required by the driver; and a torque difference mode in
which priority is given to the generation of a difference .DELTA.T
(hereinafter referred to as torque difference .DELTA.T) in the
torques applied to the rear wheels 4L and 4R during cornering. In
this embodiment, the stepping acceleration .alpha. (a second-order
time differentiation value of the accelerator position AP) of the
accelerator pedal 9 during cornering is used as the driving
operation by the driver, and the steering angle .theta. is used the
determination of the turning direction.
[0036] "Priority" refers to the degree (rate) of the priority. The
priority affects "the rate of an actual target output (torque
instruction value) to the output required by the driver" and "the
rate of an actual torque difference of the left and right wheels to
the torque difference .DELTA.T optimal for the cornering." The
priority can be expressed in percentage: for example, the demand
torque mode is expressed by the priority of 30% and the torque
difference mode is expressed by the priority of 70%.
[0037] The stepping acceleration .alpha. of the accelerator pedal 9
corresponds to the degree of acceleration required by the driver
(degree of acceleration requirement). That is, when the degree of
acceleration required by the driver is large, since the accelerator
pedal 9 is swiftly stepped by the driver, the stepping acceleration
.alpha. becomes large. When the degree of acceleration required by
the driver is small, since the accelerator pedal 9 is slowly
stepped by the driver, the stepping acceleration .alpha. becomes
small.
[0038] A driving-force control according to this embodiment for
determining the one of two control modes to the priority of either
0% or 100% and the other of two control modes to the priority of
either 100% or 0% depending on the driving operation by the driver
will now be described. That is, the driving-force control according
to this embodiment selects one of the control modes set to the
priority of 100% and then switches to the other control mode that
is reset to the priority of 100%; i.e., the modes are switched
depending on the driving operation by the driver.
[0039] The demand torque mode gives priority of the generation of
the demand torque Tr by the motors 2L and 2R in response to the
accelerator position AP during cornering over the generation of the
torque difference .DELTA.T. The demand torque mode is determined
the priority of 100% when the stepping acceleration .alpha. is
equal to or larger than a predetermined value .alpha..sub.0 (while
the torque difference mode is determined the priority of 0%). That
is, high stepping acceleration .alpha. of the accelerator pedal 9
stepped by the driver is interpreted as the intent of the driver to
change the traveling direction of the vehicle 1 during acceleration
(i.e., an increase in the driving force) regardless of spinning of
the vehicle 1, and gives priority of the generation of the output
required by the driver. In the demand torque mode, the motors 2 are
controlled such that a total torque Tt of the output torque TL from
the left motor 2L and the output torque TR from the right motor 2R
equals the demand torque Tr. In the demand torque mode, the
difference between the output torques TL and TR may be smaller than
the torque difference .DELTA.T.
[0040] The torque difference mode gives priority of the generation
of an ideal torque difference .DELTA.T generated by the motors 2L
and 2R to maintain high stability during cornering over the
generation of the demand torque Tr. The torque difference mode is
determined the priority of 100% when the stepping acceleration
.alpha. is smaller than the predetermined value .alpha..sub.0
(while the demand torque mode is determined the priority of 0%).
That is, low stepping acceleration .alpha. of the accelerator pedal
9 stepped by the driver is interpreted as the intent of the driver
to pass through a curve at the current vehicle speed (no intent of
intense acceleration) and gives priority of the generation of an
ideal torque difference .DELTA.T. In the torque difference mode,
the motors 2 are controlled such that the output torque transmitted
from the motor 2 to the turning outer wheel is greater by the
torque difference .DELTA.T than the output torque transmitted from
the motor 2 to the turning inner wheel. In the torque difference
mode, the total torque Tt of the output torques TL and TR may be
smaller than the demand torque Tr.
[0041] With reference to FIGS. 1 and 2, the ECU 10 includes
functional components for carrying out the driving-force control
described above, i.e., a calculator 11 (computing unit) and a
controller 12 (control unit). The calculator 11 includes a
demand-torque calculator 11a, a torque-difference calculator 11b, a
torque-difference-maintaining-torque calculator 11c, and an
indication-torque calculator 11d. These components may be provided
as electronic circuits (hardware) or software programs.
Alternatively, part of the functions may be provided as hardware
while the other functions provided as software.
[0042] The demand-torque calculator 11a calculates the demand
torque Tr corresponding to the stepping operation amount
(accelerator position AP) of the accelerator pedal 9 stepped by the
driver and is constantly in a calculation mode when the ECU 10 is
turned on regardless of the cornering of the vehicle 1. The
demand-torque calculator 11a acquires the demand torque Tr
corresponding to the accelerator position AP detected by the
accelerator position sensor 16 using the map illustrated in FIG.
3A. The demand-torque calculator 11a sends the calculated demand
torque Tr to the torque-difference-maintaining-torque calculator
11c and the indication-torque calculator 11d.
[0043] FIG. 3B illustrates the output characteristics of the motors
2L and 2R according to this embodiment. With reference to FIG. 3B,
each output of the motors 2L and 2R according to this embodiment
linearly increases as the accelerator position AP increases. That
is, in the output characteristics of the motors 2L and 2R, zero
torque is output at the accelerator position AP of 0% and maximum
output torques TL.sub.MAX and TR.sub.MAX are output at the
accelerator position AP of 100%. The maximum output torques
TL.sub.MAX and TR.sub.MAX of the respective motors 2L and 2R are
identical. Thus, hereinafter maximum output torques TL.sub.MAX and
TR.sub.MAX are simply referred to as maximum output torque
T.sub.MAX.
[0044] The torque-difference calculator 11b calculates the ideal
torque difference .DELTA.T during cornering that enables stable
cornering. The torque-difference calculator 11b calculates the
torque difference .DELTA.T, for example, on the basis of the
steering angle .theta. detected by the steering angle sensor 15 and
a vehicle speed V calculated from the wheel rotating speeds
detected by the wheel-speed sensors 13L, 13R, 14L, and 14R. The
torque-difference calculator 11b sends the calculated torque
difference .DELTA.T to the torque-difference-maintaining-torque
calculator 11c.
[0045] The torque-difference-maintaining-torque calculator 11c
calculates the torques to be output from the motors 2L and 2R when
generating the demand torque Tr calculated by the demand-torque
calculator 11a while maintaining the torque difference .DELTA.T
calculated by the torque-difference calculator 11b (hereinafter
these torques are referred to as torque-difference maintaining
torques TL.sub.K and TR.sub.K). The
torque-difference-maintaining-torque calculator 11c sends the
calculated torque-difference maintaining torques TL.sub.K and
TR.sub.K to the indication-torque calculator 11d.
[0046] For example, in clockwise turning of the vehicle 1, the left
rear wheel 4L is the turning outer wheel and the right rear wheel
4R is the turning inner wheel. Thus, the torque-difference
maintaining torque TL.sub.K generated in the left motor 2L can be
represented by Expression (1a), and the torque-difference
maintaining torque TR.sub.K generated in the right motor 2R can be
represented by Expression (1b). In counterclockwise turning, the
torque-difference maintaining torques TL.sub.K and TR.sub.K are
reversed. That is, in the counterclockwise turning of the vehicle
1, the torque-difference maintaining torque TL.sub.K generated in
the left motor 2L is represented by the right side of Expression
(1b), and the torque-difference maintaining torque TR.sub.K
generated in the right motor 2R is represented by the right side of
Expression (1a).
Expression 1 TL K = Tr 2 + .DELTA. T 2 , ( 1 a ) TR K = Tr 2 -
.DELTA. T 2 ( 1 b ) ##EQU00001##
[0047] The indication-torque calculator 11d calculates the output
torques TL and TR (torque instruction values) instructing the
motors 2L and 2R depending on the torque-difference maintaining
torques TL.sub.K and TR.sub.K, the stepping acceleration .alpha.,
and the steering angle .theta. and sets the output torques TL and
TR. The output torques TL and TR set by the indication-torque
calculator 11d are sent to the controller 12. The indication-torque
calculator 11d compares the maximum output torque T.sub.MAX of the
motors 2 with the torque Tout.sub.K, which is the larger one of the
torque-difference maintaining torques TL.sub.K and TR.sub.K
calculated by the torque-difference-maintaining-torque calculator
11c (the torque-difference maintaining torque of the turning outer
wheel).
[0048] If the torque-difference maintaining torque Tout.sub.K of
the turning outer wheel is less than or equal to the maximum output
torque T.sub.MAX, the torque-difference maintaining torques
TL.sub.K and TR.sub.K can be generated by the motors 2L and 2R,
respectively. In this case, the demand torque Tr can be achieved
with the torque difference .DELTA.T generated by the motors 2L and
2R. Thus, the indication-torque calculator 11d sets the respective
output torques TL and TR to the torque-difference maintaining
torques TL.sub.K and TR.sub.K (TL=TL.sub.K, TR=TR.sub.K).
[0049] If the torque-difference maintaining torque Tout.sub.K of
the turning outer wheel exceeds the maximum output torque
T.sub.MAX, the torque Tout.sub.K cannot be generated by the motors
2. In such a case, the indication-torque calculator 11d subtracts
the maximum output torque T.sub.MAX from the torque Tout.sub.K to
calculate the excess D over the maximum output torque T.sub.MAX
(D=Tout.sub.K-T.sub.MAX). The turning direction is determined based
on positive and negative of the steering angle .theta., and the
output torque from the motor 2 of the turning outer wheel is set to
the maximum output torque T.sub.MAX of the motors 2 (i.e., the
value obtained by subtracting the excess D from the
torque-difference maintaining torque Tout.sub.K of the turning
outer wheel).
[0050] The indication-torque calculator 11d calculates the
second-order time differentiation value of the accelerator position
AP to obtain the stepping acceleration .alpha., determines the
priorities of the two control modes depending on the stepping
acceleration .alpha., and sets the output torque from the motor 2
of the turning inner wheel based on the determined priorities. In
this embodiment, when the stepping acceleration .alpha. is equal to
or larger than the predetermined value .alpha..sub.0, the demand
torque mode is determined the priority of 100% and the torque
difference mode is determined the priority of 0%. When the stepping
acceleration .alpha. is smaller than the predetermined value
.alpha..sub.0, the demand torque mode is determined the priority of
0% and the torque difference mode is determined the priority of
100%. The predetermined value .alpha..sub.0 is a threshold to
determine the degree of acceleration requirement of the driver
(acceleration intent) during cornering and may be a preset value or
may be set to any value in advance by the driver.
[0051] If the priority of the demand torque mode is 100%, the
indication-torque calculator 11d sets the output torque of the
turning inner wheel to the sum of the corresponding
torque-difference maintaining torque and the excess D. That is, the
output torque of the turning inner wheel is set to the sum of the
smaller one of the torque-difference maintaining torques TL.sub.K
and TR.sub.K and the difference obtained by subtracting the maximum
output torque T.sub.MAX from the torque-difference maintaining
torque Tout.sub.K of the turning outer wheel. Such setting
generates the demand torque Tr by the motors 2L and 2R and
approximates, as much as possible, the torque difference .DELTA.T
to the difference between the output torques TL and TR.
[0052] For example, if the priority of the demand torque mode is
100% in the clockwise turning, the indication-torque calculator 11d
sets the output torque TL from the left motor 2L to the maximum
output torque T.sub.MAX (the difference obtained by subtracting the
excess D from the left torque-difference maintaining torque
TL.sub.K (TL=TL.sub.K-D=T.sub.MAX)) and the output torque TR from
the right motor 2R to the sum of the right torque-difference
maintaining torque TR.sub.K and the excess D (TR=TR.sub.K+D). In
contrast, in the counterclockwise turning, the output torque TR
from the right motor 2R is set to the maximum output torque
T.sub.MAX (the difference obtained by subtracting the excess D from
the right torque-difference maintaining torque TR.sub.K
(TR=TR.sub.K-D=T.sub.MAX)), and the output torque TL from the left
motor 2L is set to the sum of the left torque-difference
maintaining torque TL.sub.K and the excess D (TL=TL.sub.K+D).
[0053] By such setting of the output torques TL and TR, the total
torque Tt is not changed. Consequently, the motors 2L and 2R can
generate the demand torque Tr. Although the difference between the
output torques TL and TR is smaller than the ideal torque
difference .DELTA.T, the difference between the torques TL and TR
can be maximized by setting the output torque of turning outer
wheel to the maximum output torque T.sub.MAX.
[0054] On the other hand, if the priority of the torque difference
mode is 100%, the indication-torque calculator 11d sets the output
torque of the turning inner wheel to the difference obtained by
subtracting the excess D from the corresponding torque-difference
maintaining torque (i.e., the smaller one of the torque-difference
maintaining torques TL.sub.K and TR.sub.K). That is, in the torque
difference mode, the output torques TL and TR are set to the
differences obtained by subtracting the excess D from the
respective torque-difference maintaining torques TL.sub.K and
TR.sub.K (TL=TL.sub.K-D, TR=TR.sub.K-D), regardless of the turning
direction. In this way, the output torques TL and TR are set while
keeping the torque difference .DELTA.T between the
torque-difference maintaining torques TL.sub.K and TR.sub.K. In the
torque difference mode, the output torque of the turning outer
wheel is set to the maximum output torque T.sub.MAX, and thus the
total torque Tt can approximate the demand torque Tr as much as
possible.
[0055] If the steering angle .theta. detected by the steering angle
sensor 15 is less than or equal to a predetermined steering angle
.theta..sub.0, the indication-torque calculator 11d determines a
non-cornering mode. Then, the indication-torque calculator 11d sets
each of the output torques TL and TR to half of the demand torque
Tr calculated by the demand-torque calculator 11a (TL=TR=Tr/2). The
predetermined steering angle .theta..sub.0 is a threshold to
determine a variation in the traveling direction of the vehicle 1
and may be a preset value approximating zero or a value set
depending on the speed and acceleration of the vehicle.
[0056] The controller 12 controls the motors 2L and 2R by
instructing them to generate the output torques TL and TR set by
the indication-torque calculator 11d.
1-3. Flow Chart
[0057] FIG. 4 is a flow chart illustrating the process of
driving-force control. The process in the flow chart is repeated at
a predetermined calculation cycle while the ECU 10 is turned
on.
[0058] With reference to FIG. 4, in Step S10, the data items
detected by the sensors 13 to 16 are input to the ECU 10. In Step
S20, the demand-torque calculator 11a calculates the demand torque
Tr. In Step S30, the steering angle .theta. is determined whether
to be larger than the predetermined steering angle
.theta..sub.0.
[0059] If the vehicle 1 is not cornering. Thus, the process goes to
Step S140. In Step S140, the indication-torque calculator 11d sets
each of the output torques TL and TR to half of the demand torque
Tr. If .theta.>.theta..sub.0, the torque-difference calculator
11b calculates the torque difference .DELTA.T in Step S40. In Step
S50, the torque-difference-maintaining-torque calculator 11c
calculates the torque-difference maintaining torques TL.sub.K and
TR.sub.K.
[0060] Step S60 and the subsequent steps are performed by the
indication-torque calculator 11d. In Step S60, the
torque-difference maintaining torque Tout.sub.K of the turning
outer wheel is determined whether to be larger than the maximum
output torque T.sub.MAX. If T.sub.out.sub.K.ltoreq.T.sub.MAX, the
torque-difference maintaining torques TL.sub.K and TR.sub.K can
both be generated. Thus, the process goes to Step S130 to set the
respective output torques TL and TR to the torque-difference
maintaining torques TL.sub.K and TR.sub.K calculated in Step
S50.
[0061] If T.sub.out.sub.K>T.sub.MAX, the excess D is calculated
in Step S70. In Step S80, the stepping acceleration .alpha.
calculated from the accelerator position AP is determined whether
to be equal to or larger than the predetermined value
.alpha..sub.0. If .alpha.<.alpha..sub.0, the torque difference
mode is determined to the priority of 100%, and the process goes to
Step S120. In Step S120, the respective output torques TL and TR
are set to the differences obtained by subtracting the excess D
calculated in Step S70 from the respective torque-difference
maintaining torques TL.sub.K and TR.sub.K calculated in Step
S50.
[0062] If .alpha..gtoreq..alpha..sub.0, the priority of 100% is
determined to the demand torque mode, and the turning direction is
determined from the steering angle .theta.. In Step S90, the
turning is determined whether to be the clockwise turn. If the
clockwise turning, in Step S110, the output torque TL from the left
motor 2L of the turning outer wheel is set to the maximum output
torque T.sub.MAX of the motors 2 (i.e., the difference obtained by
subtracting the excess D from the left torque-difference
maintaining torques TL.sub.K), and the output torque TR from the
right motor 2R of the turning inner wheel is set to the sum of the
right torque-difference maintaining torques TR.sub.K and the excess
D. If the counterclockwise turning, in Step S100, the output torque
TR from the right motor 2R of the turning outer wheel is set to the
maximum output torque T.sub.MAX of the motors 2 (i.e., the
difference obtained by subtracting the excess D from the right
torque-difference maintaining torques TR.sub.K), and the output
torque TL from the left motor 2L of the turning inner wheel is set
to the sum of the left torque-difference maintaining torques
TL.sub.K and the excess D.
[0063] In Step S150, the motors 2L and 2R are controlled through
instruction for the output of the output torques TL and TR set in
Steps S100 to S140. In Step S160, the ECU 10 is determined whether
to be turned on or off. If determined to be on, the process returns
to Step S10. If determined to be off, the process ends.
1-4. Advantageous Effects
[0064] The driving-force controller described above controls the
motors 2 through the determination of priorities of the demand
torque mode that generates the demand torque Tr and the torque
difference mode that generates the torque difference .DELTA.T,
depending on the driving operation of the driver. Such control can
improve the cornering performance of the vehicle 1 while achieving
the driver's request (the demand torque Tr and the total output of
the motors 2).
[0065] In particular, the driving-force controller described above
can appropriately interpret the driver's intention through the
determination of the priorities of the two control modes depending
on the stepping acceleration .alpha. of the accelerator pedal 9 and
can carry out control suitable for the driver's intention.
[0066] Specifically, the driving-force controller described above
increases the priority of the demand torque mode as the stepping
acceleration .alpha. becomes larger. High stepping acceleration
.alpha. during cornering can be interpreted as the intent (strong
degree of acceleration requirement) of the driver to change the
traveling direction of the vehicle 1 during acceleration (i.e., an
increase in the driving force). Thus, the acceleration request of
the driver can be achieved by increasing the priority of the
generation of the output required by the driver as the stepping
acceleration .alpha. increases.
[0067] The driving-force controller described above increases the
priority of the torque difference mode as the stepping acceleration
.alpha. becomes smaller. Low stepping acceleration .alpha. during
cornering can be interpreted as the intent of the driver to pass
through a curve at the current vehicle speed (weak degree of
acceleration requirement). Thus, the stability during cornering can
be increased and the cornering performance can be improved by
increasing the priority of the generation of the torque difference
.DELTA.T as the stepping acceleration .alpha. decreases.
[0068] The driving-force controller described above selects the
demand torque mode with the priority of 100% when the stepping
acceleration .alpha. is equal to or larger than the predetermined
value .alpha..sub.0 during cornering and selects the torque
difference mode with the priority of 100% when the stepping
acceleration .alpha. is smaller than the predetermined value
.alpha..sub.0 during cornering. That is, the switching between the
two control modes on the basis of the predetermined value
.alpha..sub.0 as a threshold can simplify the control
configuration.
[0069] The driving-force controller described above sets the output
torque from the motor 2 of the turning outer wheel to the maximum
output torque T.sub.MAX of the motors 2 and determines the output
torque from the motor 2 of the turning inner wheel depending on the
priorities of the control modes. This achieves the driver's request
and improves the cornering performance. For example, if the demand
torque mode is selected between the two control modes depending on
the stepping acceleration .alpha. as in this embodiment, the motors
2L and 2R generate the demand torque Tr while approximating, as
much as possible, the difference between the output torques TL and
TR to the torque difference .DELTA.T. If the torque difference mode
is selected, the torque difference .DELTA.T between the output
torques TL and TR is maintained while the total torque Tt is
approximated as much as possible to the demand torque Tr.
2. Second Embodiment
2-1. Configuration
[0070] A driving-force controller for an electric vehicle according
to a second embodiment will now be described with reference to
FIGS. 1 to 3 and FIGS. 5 to 7. The driving-force controller
according to this embodiment is applied to the vehicle 1
illustrated in FIG. 1 and includes the functional components
illustrated in FIG. 2 in the ECU 10.
[0071] The driving-force controller according to this embodiment
carries out driving-force control different from that according to
the first embodiment. The control according to this embodiment is
different from that of the first embodiment in the output
characteristics of the motors 2 and the calculation method carried
out by the indication-torque calculator 11d of the ECU 10. The
configurations that differ from the first embodiment will now be
described.
[0072] The driving-force control according to this embodiment
determines the priorities of the two control modes using a map (an
upper limit torque difference map) previously setting therein a
relationship between the driving operation by the driver and the
torque difference that can be generated during cornering (the
torque difference being generatable during cornering). That is, the
priorities according to this embodiment are set to values between
0% and 100% depending on the driving operation of the driver so
that the two control modes are carried out in appropriate
proportions, instead of determining the priorities of the two
control modes to either 0% or 100% depending on the driving
operation by the driver.
[0073] Specifically, the priority of "the rate of the actual target
output (torque instruction value) to the output required by the
driver" may be determined higher than the priority of "the rate of
the actual torque difference of the left and right wheels to the
torque difference .DELTA.T optimal for the cornering", or vice
versa. Alternatively, equal priorities may be determined to both
rates. In this embodiment, the stepping acceleration .alpha.
(degree of acceleration requirement) of the accelerator pedal 9
during cornering is used as the driving operation by the driver in
the determination of the priorities. The steering angle .theta. is
used the determination of the turning direction.
[0074] FIG. 5 illustrates the upper limit torque difference map
used in this embodiment. FIG. 5 is a map illustrating the
upper-limit torque difference .DELTA.Tp against the accelerator
position AP during cornering. The upper-limit torque difference
.DELTA.Tp linearly decreases with an increase in the accelerator
position AP. The upper-limit torque difference .DELTA.Tp means the
upper limit of the difference between the torques TL and TR output
from the motors 2L and 2R. That is, if the ideal torque difference
calculated by the torque-difference calculator 11b (referred to as
an ideal torque difference .DELTA.Ti in this embodiment) is more
than or equal to the upper-limit torque difference .DELTA.Tp, the
torque difference .DELTA.T applied to the rear wheels 4L and 4R is
clipped at the upper-limit torque difference .DELTA.Tp. In
contrast, if the ideal torque difference .DELTA.Ti is less than the
upper-limit torque difference .DELTA.Tp, the torque difference
.DELTA.T applied to the rear wheels 4L and 4R equals the ideal
torque difference .DELTA.Ti.
[0075] The motors 2L and 2R according to this embodiment have
identical output characteristics and can operate in a powered mode
and a regenerative mode, as in the first embodiment. Thus, if one
of the motors 2 operates in the powered mode at a maximum output
torque T.sub.MAX and the other motor 2 operates in the regenerative
mode at the maximum output torque T.sub.MAX, the torque difference
that can be generated is twice the maximum output torque T.sub.MAX.
The output torque (driving force) at this time is zero. With
reference to FIG. 5, the upper-limit torque difference .DELTA.Tp is
set to twice the maximum output torque T.sub.MAX at an accelerator
position AP of 0% (achievable torque difference). Since when the
accelerator position AP is 100% the demand torque Tr is large, the
output torques TL and TR from the respective motors 2L and 2R are
large. Thus, the upper-limit torque difference .DELTA.Tp is
minimized at the accelerator position AP of 100%. This minimum is
set to different values depending on the stepping acceleration
.alpha..
[0076] With reference to FIG. 5, the upper-limit torque difference
.DELTA.Tp against the accelerator position AP is set to vary
depending on the stepping acceleration .alpha.. In this embodiment,
at a constant accelerator position AP, the upper-limit torque
difference .DELTA.Tp is set to minimize at the stepping
acceleration .alpha. being equal to or larger than the
predetermined value .alpha..sub.0 (.alpha..gtoreq..alpha..sub.0),
is set to increase as the stepping acceleration .alpha. decreases,
and is set to maximize at the stepping acceleration .alpha. of zero
(.alpha.=0). The predetermined value .alpha..sub.0 is identical to
that according to the first embodiment. The minimum of the
upper-limit torque difference .DELTA.Tp at the accelerator position
AP of 100% is set to increase as the stepping acceleration .alpha.
decreases. The reduction in the upper-limit torque difference
.DELTA.Tp relative to the increase in the accelerator position AP
(i.e., the variation in the upper-limit torque difference
.DELTA.Tp) is set to increase as the stepping acceleration .alpha.
decreases.
[0077] The graph illustrating the upper-limit torque difference
.DELTA.Tp at the stepping acceleration .alpha. being equal to or
larger than the predetermined value .alpha..sub.0 represents the
difference between the output torques TL and TR from the motors 2L
and 2R with the output torques TL and TR set such that the total
torque Tt equals the demand torque Tr. That is, the graph
illustrates the torque difference that can be generated (achievable
torque difference) at the maximum output torque T.sub.MAX at the
accelerator position AP of 100%, without limitation on outputs from
the motors 2. The graph illustrating the upper-limit torque
difference .DELTA.Tp at the stepping acceleration .alpha. of zero
is set to be larger than the maximum ideal torque difference
.DELTA.Ti that can be calculated by the torque-difference
calculator 11b.
[0078] As a result, the smaller the stepping acceleration .alpha.
is, the larger the upper-limit torque difference .DELTA.Tp is, even
at a constant accelerator position AP. Thus, the smaller the
stepping acceleration .alpha. is, the lower the possibility of the
clipping of the calculated ideal torque difference .DELTA.Ti at the
upper-limit torque difference .DELTA.Tp is. Thus, the priority is
determined to the generation of the torque difference .DELTA.T
approximating the ideal torque difference .DELTA.Ti at the rear
wheels 4L and 4R rather than the increase of the output torques TL
and TR to approximate the demand torque Tr. In other words, as the
stepping acceleration .alpha. decreases, the priority of the torque
difference mode increases and the priority of the demand torque
mode decreases. At zero stepping acceleration .alpha., the graph
with the smallest variation is selected, and the output torques TL
and TR are set to maintain the ideal torque difference .DELTA.Ti.
Thus, at zero stepping acceleration .alpha., the torque difference
mode is determined the priority of 100%.
[0079] In contrast, the larger the stepping acceleration .alpha.
is, the smaller the upper-limit torque difference .DELTA.Tp is,
even at a constant accelerator position AP. Thus, the larger
stepping acceleration .alpha. is, the higher possibility of the
clipping of the calculated ideal torque difference .DELTA.Ti at the
upper-limit torque difference .DELTA.Tp is. Thus, the priority is
determined to the increase of the output torques TL and TR to
approximate the demand torque Tr rather than the generation of the
torque difference .DELTA.T approximating the ideal torque
difference .DELTA.Ti at the rear wheels 4L and 4R. In other words,
as the stepping acceleration .alpha. increases, the priority of the
demand torque mode increases and the priority of the torque
difference mode decreases. At the stepping acceleration .alpha.
being equal to or larger than the predetermined value
.alpha..sub.0, the graph with the largest variation is selected,
and the output torques TL and TR are set such that the total torque
Tt equals the demand torque Tr and then the upper-limit torque
difference .DELTA.Tp is applied. Thus, at the stepping acceleration
.alpha. being equal to or larger than the predetermined value
.alpha..sub.0, the demand torque mode is determined the priority of
100%.
[0080] For the generation of the upper-limit torque difference
.DELTA.Tp illustrated in FIG. 5, the output characteristics of the
motors 2 according to this embodiment are set to vary depending on
the accelerator position AP and the stepping acceleration .alpha.,
as illustrated in FIG. 6. As illustrated in the output
characteristics map in FIG. 6, the output torque linearly increases
with an increase in the accelerator position AP. The output torque
is set to zero for the accelerator position AP of 0%, whereas the
output torque is set to maximize at the accelerator position AP of
100%. The maximum value is set to different values depending on the
stepping acceleration .alpha..
[0081] With reference to FIG. 6, the output torque against the
accelerator position AP sets to vary depending on the stepping
acceleration .alpha.. The output torque at the accelerator position
AP of 100% (i.e., the maximum value of the output torque) is set to
the maximum output torque T.sub.MAX of the motors 2 at the stepping
acceleration .alpha. being equal to or larger than the
predetermined value .alpha..sub.0. The maximum value of the output
torque is set to a smaller value for lower stepping acceleration
.alpha.. That is, the maximum output torque of the motors 2
according to this embodiment is set to a value smaller than the
maximum output torque T.sub.MAX of the motors 2 as the stepping
acceleration .alpha. becomes smaller than the predetermined value
.alpha..sub.0, and the torque has a margin even at an accelerator
position AP of 100%. In other words, the outputs of the motors 2
are more limited as the stepping acceleration .alpha. decreases.
This generates the upper-limit torque difference .DELTA.Tp
illustrated in FIG. 5.
[0082] FIGS. 5 and 6 are maps that illustrates three graphs between
the graphs for .alpha.=0 and .alpha..gtoreq..alpha..sub.0. Many
graphs are provided between the graphs for .alpha.=0 and
.alpha..gtoreq..alpha..sub.0 and the graph corresponding to the
stepping operation acceleration .alpha. is selected. FIGS. 5 and 6
illustrate two-dimensional maps. Alternatively, the stepping
operation acceleration .alpha. may be added to create a
three-dimensional map.
[0083] The calculator 11 of the ECU 10 will now be described. The
calculation method carried out by the demand-torque calculator 11a,
the torque-difference calculator 11b, and the
torque-difference-maintaining-torque calculator 11c are the same as
those according to the first embodiment. The torque-difference
calculator 11b according to this embodiment sends the calculated
torque difference as the ideal torque difference .DELTA.Ti to the
torque-difference-maintaining-torque calculator 11c. The
torque-difference-maintaining-torque calculator 11c replaces the
torque differences .DELTA.T in Expressions (1a) and (1b) with the
ideal torque differences .DELTA.Ti sent from the torque-difference
calculator 11b to calculate the torque-difference maintaining
torques TL.sub.K and TR.sub.K.
[0084] The indication-torque calculator 11d, as in the first
embodiment, calculates and sets the output torques TL and TR
(torque instruction values) instructing the motors 2L and 2R and
sends the output torques TL and TR to the controller 12. In this
embodiment, the indication-torque calculator 11d calculates the
output torques TL and TR using the maps illustrated in FIGS. 5 and
6.
[0085] The indication-torque calculator 11d applies the stepping
acceleration .alpha. during cornering to the output characteristics
map in FIG. 6, selects the graph corresponding to the stepping
acceleration .alpha., and acquires the maximum output torque of the
graph (the maximum output torque corresponding to the stepping
acceleration .alpha.). In this way, the upper-limit torque
difference .DELTA.Tp corresponding to the stepping acceleration
.alpha. can be generated even at the accelerator position AP of
100%. That is, the output torques of the motors 2 have margins to
secure the upper-limit torque difference .DELTA.Tp corresponding to
the stepping acceleration .alpha.. Hereinafter, N denotes the graph
corresponding to the stepping acceleration .alpha., and Tm denotes
the maximum output torque of the graph N. Although FIGS. 5 and 6
illustrate an example graph N and FIG. 5 illustrates an example
maximum output torque Tm, the graph N and the maximum output torque
Tm should not be limited to those illustrated in the drawings.
[0086] The indication-torque calculator 11d compares the
torque-difference maintaining torque Tout.sub.K of the turning
outer wheel calculated by the torque-difference-maintaining-torque
calculator 11c with the acquired maximum output torque Tm of the
motors 2. If the torque-difference maintaining torque Tout.sub.K of
the turning outer wheel is less than or equal to the maximum output
torque Tm, the torque-difference maintaining torques TL.sub.K and
TR.sub.K can be generated by the respective motors 2L and 2R. In
this case, the demand torque Tr can be achieved with the ideal
torque difference .DELTA.Ti generated by the motors 2L and 2R.
Thus, the indication-torque calculator 11d sets the respective
output torques TL and TR to the torque-difference maintaining
torques TL.sub.K and TR.sub.K (TL=TL.sub.K, TR=TR.sub.K).
[0087] If the torque-difference maintaining torque T.sub.out.sub.K
of the turning outer wheel exceeds the maximum output torque Tm,
the torque Tout.sub.K cannot be generated by the motors 2. Thus,
the indication-torque calculator 11d determines the priorities of
the demand torque mode and the torque difference mode depending on
the stepping acceleration .alpha.. Specifically, the
indication-torque calculator 11d acquires the upper-limit torque
difference .DELTA.Tp corresponding to the priorities of the two
control modes through the application of the stepping acceleration
.alpha. and the accelerator position AP to the map in FIG. 5. The
indication-torque calculator 11d compares the acquired upper-limit
torque difference .DELTA.Tp with the ideal torque difference
.DELTA.Ti calculated by the torque-difference calculator 11b.
[0088] If the ideal torque difference .DELTA.Ti is more than or
equal to the upper-limit torque difference .DELTA.Tp, the
indication-torque calculator 11d clips the torque difference
.DELTA.T at the upper-limit torque difference .DELTA.Tp
(.DELTA.T=.DELTA.Tp). That is, the demand torque mode is determined
the priority higher than the priority determined to the torque
difference mode. If the ideal torque difference .DELTA.Ti is less
than the upper-limit torque difference .DELTA.Tp, the
indication-torque calculator 11d sets the torque difference
.DELTA.T to the ideal torque difference .DELTA.Ti
(.DELTA.T=.DELTA.Ti). That is, the torque difference mode is
determined the priority higher than the priority of the demand
torque mode.
[0089] The indication-torque calculator 11d determines the turning
direction based on positive and negative of the steering angle
.theta. and sets the output torque from the motor 2 of the turning
outer wheel to the acquired maximum output torque Tm. The
indication-torque calculator 11d sets the output torque from the
motor 2 of the turning inner wheel to the difference obtained by
subtracting the torque difference .DELTA.T from the acquired
maximum output torque Tm. The torque difference .DELTA.T is set on
the basis of the priorities determined depending on the stepping
acceleration .alpha.. Thus, setting the output torque of the
turning inner wheel in this way can supply the output torques TL
and TR corresponding to the priorities of the two control modes to
the respective rear wheels 4L and 4R.
[0090] Specific examples of the setting of the output torque of the
turning inner wheel will now be described. For example, if the
stepping acceleration .alpha. during cornering is zero, the
indication-torque calculator 11d selects the graphs having the
smallest variation in the maps in FIGS. 5 and 6. The upper-limit
torque difference .DELTA.Tp acquired from FIG. 5 is larger than the
ideal torque difference .DELTA.Ti calculated by the
torque-difference calculator 11b regardless of the accelerator
position AP. Thus, the indication-torque calculator 11d sets the
torque difference .DELTA.T to the ideal torque difference
.DELTA.Ti. As a result, the output torque of the turning inner
wheel is set to the difference obtained by subtracting the torque
difference .DELTA.T (ideal torque difference .DELTA.Ti) from the
output torque of the turning outer wheel (i.e., the maximum output
torque corresponding to the current stepping acceleration .alpha.
(.alpha.=0)). Thus, the ideal torque difference .DELTA.Ti
calculated by the torque-difference calculator 11b is secured, and
the torque difference mode is determined the priority of 100%.
[0091] If the stepping acceleration .alpha. during cornering equals
.alpha..sub.0, the indication-torque calculator 11d selects the
graphs having the largest variation in the maps in FIGS. 5 and 6.
The upper-limit torque difference .DELTA.Tp acquired from FIG. 5 is
smaller than the ideal torque difference .DELTA.Ti calculated by
the torque-difference calculator 11b depending on the accelerator
position AP. Thus, if the ideal torque difference .DELTA.Ti is more
than or equal to the upper-limit torque difference .DELTA.Tp, the
indication-torque calculator 11d sets the torque difference
.DELTA.T to the upper-limit torque difference .DELTA.Tp. As a
result, the output torque of the turning inner wheel is set to the
difference obtained by subtracting the torque difference .DELTA.T
(upper-limit torque difference .DELTA.Tp) from the output torque of
the turning outer wheel (i.e., the maximum output torque T.sub.MAX
corresponding to the current stepping acceleration .alpha.
(.alpha.=.alpha..sub.0)). Thus, the demand torque Tr is secured,
and the demand torque mode is determined the priority of 100%.
[0092] If the steering angle .theta. detected by the steering angle
sensor 15 is less than or equal to the predetermined value
.theta..sub.0, the indication-torque calculator 11d determines a
non-cornering mode, as in the first embodiment, and sets the output
torques TL and TR to half of the demand torque Tr (TL=TR=Tr/2).
2-2. Flow Chart
[0093] FIG. 7 is a flow chart illustrating the process of
driving-force control according to this embodiment. The process in
the flow chart is repeated at a predetermined calculation cycle
while the ECU 10 is turned on.
[0094] With reference to FIG. 7, in Step X10, the data items
detected by the sensors 13 to 16 are input to the ECU 10. In Step
X20, the demand-torque calculator 11a calculates the demand torque
Tr.
[0095] In Step X30, the steering angle .theta. is determined
whether to be larger than the predetermined value .theta..sub.0. If
.theta..ltoreq..theta..sub.0, the process goes to Step X140. In
Step X140, the indication-torque calculator 11d sets each of the
output torques TL and TR to half of the demand torque Tr. If
.theta.>.theta..sub.0, the torque-difference calculator 11b
calculates the ideal torque difference .DELTA.Ti in Step X40. In
Step X50, the torque-difference-maintaining-torque calculator 11c
calculates the torque-difference maintaining torques TL.sub.K and
TR.sub.K.
[0096] Step X55 and the subsequent steps are performed by the
indication-torque calculator 11d. In Step X55, the stepping
acceleration .alpha. calculated from the accelerator position AP is
applied to the map of output characteristics in FIG. 6 to acquire
the maximum output torque Tm corresponding to the stepping
acceleration .alpha.. In Step X60, the torque-difference
maintaining torque Tout.sub.K of the turning outer wheel is
determined whether to be larger than the maximum output torque Tm
acquired in Step X55.
[0097] If T.sub.out.sub.K.ltoreq.Tm, the torque-difference
maintaining torques TL.sub.K and TR.sub.K can both be generated.
Thus, the process goes to Step X130 to set the respective output
torques TL and TR to the torque-difference maintaining torques
TL.sub.K and TR.sub.K calculated in Step X50.
[0098] If T.sub.out.sub.K>Tm, the stepping acceleration .alpha.
and the accelerator position AP are applied to the map in FIG. 5 in
Step X70 so as to acquire the upper-limit torque difference
.DELTA.Tp corresponding to the stepping acceleration .alpha. and
the accelerator position AP. In Step X75, the ideal torque
difference .DELTA.Ti calculated in Step X40 is determined whether
to be smaller than the upper-limit torque difference .DELTA.Tp
acquired in Step X70. If .DELTA.Ti.gtoreq..DELTA.Tp, the torque
difference .DELTA.T is set to the upper-limit torque difference
.DELTA.Tp in Step X80. If .DELTA.Ti<.DELTA.Tp, the torque
difference .DELTA.T is set to the ideal torque difference .DELTA.Ti
in Step X85. In this way, the torque difference .DELTA.T is set
depending on the stepping acceleration .alpha..
[0099] In Step X90, the turning is determined whether to be
clockwise turning. If in the clockwise turning, in Step X110, the
output torque TL from the left motor 2L of the turning outer wheel
is set to the maximum output torque Tm acquired in Step X55, and
the output torque TR from the right motor 2R of the turning inner
wheel is set to the difference obtained by subtracting the torque
difference .DELTA.T set in Step X80 or X85 from the maximum output
torque Tm acquired in Step X55. If in the counterclockwise turning,
in Step X100, the output torque TR from the right motor 2R of the
turning outer wheel is set to the maximum output torque Tm acquired
in Step X55, and the output torque TL from the left motor 2L of the
turning inner wheel is set to the difference obtained by
subtracting the torque difference .DELTA.T set in Step X80 or X85
from the maximum output torque Tm acquired in Step X55.
[0100] In Step X150, the motors 2L and 2R are controlled through
instruction for the output of the output torques TL and TR set in
Steps X100 to X140. In Step X160, the ECU 10 is determined whether
to be turned on or off. If determined to be on, the process returns
to Step X10. If determined to be off, the process ends.
2-3. Advantageous Effects
[0101] The driving-force controller according to this embodiment
determines the priorities of the two control modes using the map
(the upper limit torque difference map) previously setting therein
the relationship between the driving operation by the driver and
the torque difference that can be generated during cornering (the
torque difference being generatable during cornering). Thus, the
priorities can be determined with appropriate proportions to carry
out control suitable for the intent of the driver. The components
that are the same as those in the first embodiment achieve the same
advantages as those in the first embodiment.
3. Others
[0102] The present invention should not be limited to the
embodiments described above and may be modified in various ways
within the scope of the embodiments.
[0103] In the first embodiment, when the output torque Tout.sub.K
of the turning outer wheel exceeds the maximum output torque
T.sub.MAX of the motors 2, the output torques TL and TR may be set
in any manner other than that described above. For example, in the
demand torque mode having the priority of 100%, the output torque
from the motor 2 of the turning outer wheel may be set to a value
smaller than the maximum output torque T.sub.MAX to determine
priority of only the generation of the demand torque Tr by the
motors 2L and 2R, without the torque difference .DELTA.T.
[0104] That is, in any of the embodiments described above, if the
priority of the demand torque mode is higher than the priority of
the torque difference mode, the output torques TL and TR may be set
to determine priority of the generation of a total torque Tt
approximating the demand torque Tr rather than the generation of
the torque difference .DELTA.T, whereas if the priority of the
torque difference mode is higher than the priority of the demand
torque mode, the output torques TL and TR may be set such that
priority is determined to the generation of a torque difference
approximating the torque difference .DELTA.T rather than the
generation of the total torque Tt approximating the demand torque
Tr.
[0105] Any map other than that described above can be used for the
calculation of the torque difference .DELTA.T depending on the
priorities (FIG. 5) in the second embodiment. FIGS. 8A and 8B
illustrate modifications of the map in FIG. 5. FIG. 8A illustrates
a map that sets the upper-limit torque difference .DELTA.Tp to zero
in a relatively wide range of the accelerator position AP at
stepping acceleration .alpha. being equal to or larger than the
predetermined value .alpha..sub.0 or approximating the
predetermined value .alpha..sub.0. The map in FIG. 8A sets a
smaller upper-limit torque difference .DELTA.Tp at any stepping
acceleration .alpha. compared with the map in FIG. 5. That is, the
map in FIG. 8A determines higher priority of the demand torque
mode.
[0106] FIG. 8B illustrates a map that changes from the stepping
acceleration .alpha. to the accelerator position AP as the driving
operation by the driver. In this map, the upper-limit torque
difference .DELTA.Tp decreases with the increase of the accelerator
position AP and is constantly set to zero at any accelerator
position AP being equal to or larger than a predetermined valu--e
AP.sub.0. When the map in FIG. 8B is used, the upper-limit torque
difference .DELTA.Tp is smaller than the ideal torque difference
.DELTA.Ti, and the demand torque mode is determined the priority of
100% at the accelerator position AP equal to or larger than the
predetermined value AP.sub.0. A smaller accelerator position AP
generates a larger upper-limit torque difference .DELTA.Tp. Thus,
if the ideal torque difference .DELTA.Ti is less than the
upper-limit torque difference .DELTA.Tp, the ideal torque
difference .DELTA.Ti is determined to the torque difference
.DELTA.T, and the torque difference mode is determined the priority
of 100%. The motors 2 may be controlled through the determination
of priorities of the two control modes depending on the accelerator
position AP.
[0107] The torque difference .DELTA.T applied to the left and right
wheels may be set directly in a map including a predetermined
torque difference .DELTA.T depending on the priorities of the two
control modes, rather than the map defining the upper limit of the
torque difference .DELTA.Tp as in the FIGS. 5, 8A, and 8B.
[0108] In the embodiments described above, the stepping
acceleration .alpha. of the accelerator pedal 9 (a second-order
time differentiation value of the accelerator position AP) is used
as the degree of acceleration requirement of the driver. Any other
degree of acceleration requirement may also be employed. For
example, an accelerator opening speed (a stepping rate of the
accelerator pedal 9), which is a time differentiation value of the
accelerator position AP, may be used in place of the stepping
acceleration .alpha. in the embodiments described above. The
accelerator opening speed increases as the degree of acceleration
requirement of the driver increases. The accelerator opening speed
decreases as the degree of acceleration requirement of the driver
decreases. Thus, even with the use of the accelerator opening speed
in place of the stepping acceleration .alpha., the same
advantageous effects as those described above can be achieved.
[0109] The demand-torque calculator 11a may carry out any
calculation method to determine the demand torque Tr, such as a
calculation method using expressions in place of maps. The
torque-difference calculator 11b may also carry out any calculation
method other than those described above. For example, the torque
difference .DELTA.T may be calculated using other parameters or may
be directly determined on the map. In the embodiments described
above, the accelerator position sensor 16 detects the accelerator
position AP to calculate the stepping acceleration .alpha..
Alternatively, sensors may be provided to directly detect the
stepping acceleration .alpha. and/or the accelerator opening
speed.
[0110] The vehicle 1 may be any electric vehicle that includes at
least two motors that can independently drive the left and right
wheels. For example, the electric vehicle may be a four-wheel-drive
vehicle or may be a hybrid vehicle including an engine.
[0111] The invention thus described, it will be obvious that the
same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be obvious to one skilled in
the art are intended to be included within the scope of the
following claims.
REFERENCE SIGNS LIST
[0112] 1 electric car, vehicle (electric vehicle) [0113] 2, 2L, 2R
motor [0114] 4, 4L, 4R rear wheels (left and right wheels) [0115] 9
accelerator pedal [0116] 10 ECU (controller) [0117] 11 calculator
[0118] 11a demand-torque calculator [0119] 11b torque-difference
calculator [0120] 11c torque-difference-maintaining-torque
calculator [0121] 11d indication-torque calculator [0122] 12
controller [0123] 15 steering angle sensor (detector) [0124] 16
accelerator position sensor (detector) [0125] Tr demand torque
[0126] .DELTA.T torque difference [0127] .alpha. stepping
acceleration (degree of acceleration requirement) [0128]
.alpha..sub.0 predetermined value [0129] TL.sub.K, TR.sub.K left
and right torque-difference maintaining torques
* * * * *